As i remember and this is a few years ago the last video interview as such would be certainly the monserrat video or defintely the jukebox one as i can't think of any other official source.
As for audio 'mike read queen for an hour' would certainly be the last audio interview or near enough , but i'm certain the daily mail published an interview in the summer of 91 i remember vividly because i was delivering daily papers all those years ago and it was by David wigg.
What i can't rememeber was the content of this interview but i can't seem them publishing a interview in a daily paper 4 years after it just doesn't make sense , it would have been in there sooner.
So to conclude then in my opinion there must have been a interview with freddie in the spring or summer of 91 by David wigg.
Is there anyway we can find out?.
Freddie's final interview took place in late October 1991 in Montreux
but he is the last of July 1987 as Freddie speaks about Monsteratt Caballe and then about The Great Pretender, there is a video